Mains voltage powered consumer products, such as multimedia home networking nodes, are required for reasons of safety to have electrical isolation between mains voltage circuitry and low voltage circuitry. Despite the electrical isolation there is often a need to convey signals across the electrical isolation barrier between the mains voltage circuitry and the low voltage circuitry.
The determination of a location, such as a zero crossing point, on the mains voltage signal from the low voltage side is an example of such a need involving the conveyance of signals from the high voltage side to the low voltage side. The determination of a location on the mains voltage signal finds application, for example, in providing for synchronisation with a mains voltage cycle. Synchronisation with the mains voltage cycle may be used to provide for synchronised communication between and amongst low voltage circuits of multiple networked products, such as multimedia home networking nodes. The determination of a location on the mains voltage signal may also find application in monitoring the phase variation of a mains supply to determine whether or not the mains supply is liable to fail. For example, there may be an increased likelihood of failure in supply if there is more than a 2% variation in the phase of a mains supply from a twenty-four mean. Precautionary measures may then be taken, such as the engagement of an uninterruptable power supply.
Another example of such a need involving the conveyance of signals from the high voltage side to the low voltage side is the measurement on the low voltage side of the voltage level on the high voltage side, e.g. to determine variations in the mains supply voltage level over time.
Isolator circuits are known, but these tend to suffer from problems of high power dissipation, high expense and/or excessive size.
It is therefore an object for the present invention to provide an electrical isolator circuit that addresses at least one of the above drawbacks.